Temperature Dependent Micro-Structure of KAlF? from Solid to Molten States.

ABSTRACT: In situ high temperature X-ray diffraction and Raman spectroscopy were used to investigate the temperature dependent micro-structure of KAlF?. Density functional theory was applied to simulate the structure of crystalline KAlF? while a quantum chemistry ab initio simulation was performed to explore the structure of molten KAlF?. Two crystal polymorphs demonstrated to be present in solid KAlF?. At the temperature below 673 K, it belongs to the tetragonal crystal system within the P4/mbm space group, while the high temperature phase is attributed to the monoclinic crystal system within the P2?/m space group. Both polymorph KAlF? phases are characterized by a layered structure consisting of K? and [AlF?]3- octahedra, each of the [AlF?]3- octahedra equivalently shares four corners with other four [AlF?]3- octahedra along the layer. The layered structure became unstable at higher temperatures and crashed when the temperature exceeded the melting point. It demonstrated that the molten KAlF? consisted of predominant [AlF?]- and a small amount of [AlF?]3-. The Raman spectrum of molten KAlF? simulated by using a quantum chemistry ab initio method agreed well with the experimental Raman spectrum.

SUBMITTER: Ma N 

PROVIDER: S-EPMC6213106 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature